Exploration of vectorial charge transfer mechanism in TiO2/SrTiO3 composite under UV light illumination for the degradation of 4-Nitrophenol: A comparative study with TiO2 and SrTiO3

TiO2, SrTiO3 and SrTiO3/TiO2 composite catalysts were synthesized by sol-gel method. The PXRD results show the presence of both anatase TiO2 and cubic perovskite SrTiO3 in the composite. The UV-visible absorption spectra confirm the bandgap to be wide and it is in the range of 3 to 3.2 eV for all the three samples. The efficiency of all the photocatalysts were evaluated for the degradation of 4-Nitrophenol (4-NP) under UV light irradiation. The higher photocatalytic activity of SrTiO3/TiO2 composite was correlated to its improved photogenerated charge carrier separation efficiency which arises mainly due to the potential energy differences between the conduction band (CB) edge of SrTiO3 (-4.22 eV with respect to vacuum) with that of CB edge of TiO2 (-4.27 eV with respect to vacuum). Similar differences are also observed in the valancy band edge positions. These small differences in the band edge positions leads to a potential gradient at the interface facilitating vectorial transfer of charge carriers, thereby increasing the lifetime of the photogenerated electrons and holes. Further, a significant enhancement of catalytic activity was observed when the degradation reaction is carried out in presence of electron acceptor such as H2O2 and ammonium per sulfate.